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MRI, or magnetic resonance imaging, is a routine diagnostic procedure that employs strong electromagnets, radio-frequency waves, and powerful computers to generate two- and three-dimensional images of the body's organs, tissues, and bones. MR imaging does not use ionizing radiation (X-rays).
MR uses a large, tube-shaped magnet that creates a strong magnetic field around the patient. A radio-frequency coil is placed over the body part that is to be imaged. The magnetic field, along with applied radio-frequency waves, alters the alignment of hydrogen protons found in water molecules within the body. Computers reconstruct the images based on the radio-frequency signals emitted by the protons.
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Your physician may request an MR study for a number of reasons. MR is often used to obtain specific diagnostic information not already provided by other imaging technologies such as ultrasound, computed tomography (CT), and nuclear medicine.
MR may be needed to rule out disease and to facilitate medical, surgical, and other treatments for conditions of the brain, spinal column and spinal cord; eye, ear, nose and throat; bones, joints, and muscles; heart and blood vessels; chest and lungs; abdominal organs and digestive tract; and, kidneys, urinary tract, and pelvic organs. These conditions may include congenital and developmental disorders, genetic and metabolic diseases, infections and inflammatory conditions, traumatic and other types of injury, and vascular and blood diseases.
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You or your child may eat or drink as usual unless the MR examination requires the injection or ingestion of a contrast agent for image enhancement, if sedation or anesthesia is necessary, or if there are other special care considerations. In these situations, specific dietary restrictions and other instructions are provided by your physician in advance of the appointment.
It is very important to adhere to these instructions. Otherwise, the procedure will be rescheduled to a time and date that allows for the appropriate preparation. It is also important to notify the MR staff of any active illness, allergy, or previous drug reaction that may prevent you or your child from undergoing the examination safely.
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When you arrive at the MR suite, your appointment and registration will be confirmed by the MR scheduling coordinator. You will be asked to fill out the MR screening questionnaire on behalf of yourself and your child. All individuals who will be entering the MR room must fill out this form. We do this to screen individuals for items on or within the body such as cardiac pacemakers, metal implants and ferromagnetic objects. Some of these items may malfunction or move within the magnetic field and are considered a strong relative contraindication to having an MR exam.
After you complete the screening questionnaire, the MR nurse will ask a few questions and perform a clinical screening examination.
You or your child and all individuals entering the MR room must remove all metal objects (jewelry, for example) and electronic devices (watches, etc.) and change into hospital attire or wear clothing from home that is comfortable and free of metal (zippers, buttons, etc.). The nurse will then prepare you or your child for the MR procedure, which may include oral or intravenous sedation. Sedation is supervised by an anesthesiologist and administered by a registered nurse or nurse practitioner. Anesthesia, which is sometimes required, is administered by an anesthesiologist.
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The MR technologist positions and secures you or your child comfortably on a narrow bed within the large, doughnut-shaped magnet and adjusts the radio-frequency coil, which will be placed over, under or around the body part to be examined. The technologist then performs the MR examination with the radiologist and is in contact with the patient at all times. During the MR procedure, you or your child will hear repetitive knocking noises. It is particularly important to remain still when this happens, as the MR machine is obtaining images at those times. If the pictures are motion-free, this will help shorten the total exam time and prevent delays.
An entire MR examination may take from twenty minutes to one and a half hours depending on the type of information required by the radiologist and your physician. All patients undergoing sedation or anesthesia receive continuous vital monitoring and support.
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If an injection is required, you or your child may feel minor discomfort from the needle. MR itself is a painless procedure, in that the patient is not touched.
The magnet does emit rather loud pulsing sounds, but these can be dampened by wearing ear plugs or ear phones provided by the MR staff. In some cases, it is possible to watch a DVD through special goggles. Occasionally, claustrophobia is a problem. If you are concerned about this possibility, please contact the MR staff before your appointment for information and assistance.
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MR, like other imaging technologies in radiology, is FDA approved for its safety and effectiveness. It has been used to image patients since 1981 and no adverse biological effects have been reported from exposure to the magnetic fields or radio waves.
It is considered safe, provided all safety protocols are followed. That is why the screening form mentioned above -- meant to detect items on or within the body such as cardiac pacemakers, metal implants and ferromagnetic objects -- is so important. These objects may move during the procedure unless firmly anchored in the tissues. The magnetic fields tend to cause malfunction of programmable devices. Some devices, such as Baclofen pumps and Medos valves, can be safely imaged but may need to be switched off during the procedure or reprogrammed afterwards. Cardiac pacemakers are a strong relative contraindication to having an MR.
Some metallic devices are safely imaged but produce an "artifact" that may obscure the region of interest (orthodontic braces in patients undergoing pituitary imaging, for example).
Finally, surface or implanted objects with coiled wires can result in electrical burns due to heating and/or induction of currents as a result of radio-frequency effects.
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After the images are obtained, you are free to go and resume your normal activity.
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The interpretation of an MR examination involves the review of multiple images and often requires additional computer processing. After a careful analysis of your MR images, the radiologist will review the findings with the physician who requested the study and provide a report to him or her. Your child's physician will then discuss the results with you.
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